What is heart block?

The heartbeat is created by an electrical signal that starts in the heart’s upper right chamber (right atrium). The signal is produced in an area of specialized cells in the atrium called the sinus node.

The electrical signal moves down through the heart to the atrioventricular (AV) node, another cluster of specialized cells that is located in the center of the heart between the atria and ventricles. The AV node is sometimes referred to as an electrical relay station because its function is to slow the electrical current before it passes to the lower chambers of the heart (ventricles). From the AV node, the electrical current travels to the ventricles along special fibers embedded in the heart walls. When the current arrives in the ventricles, they contract and pump blood out to the body.

In people with heart block, also called AV block, the electrical signal that controls the heartbeat is partially or completely blocked from reaching the ventricles.

Who is at risk for heart block?

Heart block can be present at birth (congenital), but most heart block develops after birth. In general, the risk of acquired heart block increases with age, along with the incidence of heart disease.

First-degree heart block is common among well-trained athletes, teenagers, young adults, and people with a highly active vagus nerve. People with a variety of heart disease, including coronary artery disease, rheumatic heart disease, sarcoidosis or other structural heart disorders, are also at risk for developing first-degree heart block.

What causes acquired heart block?

Acquired heart block has many possible causes, including heart attack (the most common cause), heart disease, an enlarged heart (cardiomyopathy), heart failure and rheumatic fever. Sometimes heart block occurs as a result of injury to the heart during open heart surgery, as a side effect of some drugs, or after exposure to a toxin.

This information is provided by the Cleveland Clinic and is not intended to replace the medical advice of your doctor or healthcare provider. Please consult your healthcare provider for advice about a specific medical condition.